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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Padfoot on August 22, 2007, 04:28:06 AM

Title: why was the solution heated?
Post by: Padfoot on August 22, 2007, 04:28:06 AM

Hi,
In a recent practical, I synthesised Aspirin from salicylic acid and ethanoic anhydride (in precence of sulfuric acid).  The reaction needed to be heated (70-80 degees C).  I was wondering if anyone can tell me why this was needed.  Is it just a matter of a reasonable reaction rate?
Thanks for any help.
   

Title: Re: why was the solution heated?
Post by: lft123 on August 28, 2007, 03:55:03 PM

Hello,

yes heat is a kinetic factor, by increasing temperature you increase the reaction rate

Title: Re: why was the solution heated?
Post by: Walker on August 29, 2007, 11:23:19 AM

Check the energy profile of the synthesis it may be an endothermic reaction, so yeah you have to add energy until the reaction is even able to ocur (also based on kinetic energy)

Title: Re: why was the solution heated?
Post by: Yggdrasil on August 29, 2007, 02:14:31 PM

The fact that a reaction needs to be heated doesn't mean that it is endothermic.  For example, the combustion of gasoline is very exothermic.  However, the combustion (thankfully) occurs very slowly at room temperature.  You need to add energy in the form of heat or a spark in order to get the reaction going (i.e. achieve a reasonable reaction rate).

Additionally, the dissolution of salts like ammonium chloride occurs very quickly at room temperature despite the fact that the process is endothermic.  So, the thermodynamics of a reaction are not immediately applicable to the kinetics of a reaction.